The present invention relates to an abrasive dressing tool used for mechanical and chemical planarization abrasion of the surface of the work pieces as can be used for semiconductor wafers or the like which require precise, planar and micro polishing, and a method for manufacturing the same dressing tool. Specifically, it relates to an abrasive dressing tool and a method for manufacturing the same dressing tool, wherein ultimately micro-scratches on wafers can be drastically reduced, the rate of inferior finished products or wafers can be decreased and abrasive life time of the tool can be prolonged, by sintering and brazing diamond particles with a nickel based brazing metal on the abrasive tool and then filling or covering the non-sintered parts and re-crystallized parts of sintered and brazed layers through electroplating process.
The semiconductor industry keeps increasing its pace of development and particularly, intensive research is being concentrated on the high integration of circuits. In order to increase the rate of production in terms of the chips per unit area, multi-layered arrangement of circuits is required, which in turn is recognized to need an extensive planarization polishing of wafers as an essential process. This process is called Chemical Mechanical Planarization or CMP.
The CMP process is the process in which the circuits on wafers are subjected to planarization polishing while the wafers are rotated under a fixed pressure, with polishing pads supplied with slurry solution (polishing solution). The polishing pads used in that process are generally polyurethane-based plastic having a number of micro-pores to retain slurry solution, so that a predetermined polishing efficiency (rate of material removal) and uniform polishing may be attained.
In continuous polishing operations, however, the micro-pores on polishing pads are plugged with polishing residues due to high pressure and rotation, with the result that the polishing pads lose the original function of retaining slurry solution and so uniform polishing efficiency is not attained.
Thus, in order to cope with the plugging of micro-pores on polishing pads, there is employed a conditioning operation in which so-called conditioners consisting of stainless- or nickel plates with diamond particles fixed on them are used to micro-abrade the surface of pads for developing or forming new micro-pores.
These conditioners are classified as the metal-brazed conditioners which comprise the diamond particles fixed on stainless plates, obtained by arranging diamond particles in a mono-layer on the plates and sintering them together with mixed metal powder under a high temperature to fix the diamond, with a part of the diamond covered by brazed metals, and as the electroplated conditioners comprising diamond particles fixed on the plates by means of electroplating.
However, these two types of products have their relative disadvantages.
In the case of metal brazed conditioners, for example, the conditioners as disclosed in the U.S. Pat. No. 3,894,673, which are obtained by high temperature sintering through use of nickel-based brazing birder, are excellent in their holding force compared to the electroplated conditioners and have a good polishing effect mainly due to many chip pockets. However, because the diamond suffers from thermal damage over 800xc2x0 C., the metal components are apt to fail to reach a high-temperature sintering under complete fusion, causing unsatisfactory sintered quality. Consequently the surface of conditioners is rough and a part of the metal remains unvaryingly in the form of particles, so that metal components on metal brazed conditioners are easily broken or fallen out during abrasive dressing operation, ultimately causing micro-scratches or contamination on wafers due to the coarse particles containing or contaminated polishing pads in a CMP process.
Because in comparison with the size of the polishing particles contained in the polishing slurry solution is in the order of nanometers, the size of the metal particles fallen out from conditioner tools are tens to hundreds times that size, a serious damage by micro-scratches can be inflicted on the circuits on wafers.
On the other hand, the disadvantage of the electroplated conditioners lies in that as the bonding between the electroplated nickel layer and the diamond particles is a kind of mechanical bonding by van der Waals force which is not large enough to hold strong the diamond particles, the risk of falling-out for the diamond particles is very high, whereby the life time of conditioners is relatively short. Another drawback with these conditioners is the low polishing efficiency owing to the lack of chip pockets, which serve as channels for discharging polishing residues.
The prevention of causing scratches on wafers in a CMP process and extending the polishing life time of conditioners are becoming an important issue, because of the current trend of scaling-up of wafers to the diameter of more than 300 mm for high integrated wafers like over 256 mega DRAM in the semiconductor industry. Therefore, there is an urgent demand for an abrasive dressing tool which can satisfy not only the requirement of prolonging the abrasive life time through the improvement in the force for holding diamond particles but also the requirement of recovering high yield of chips from wafers through the decrease in micro-scratch generation and concurrent inferiority rate.
The present invention seeks to resolve the problems with prior art and so is intended to sinter and braze diamond particles with nickel-based metal for strong bonding force, so that the diamond particles may be free of the risk of falling-out.
Simultaneously, the present invention is intended to reduce micro-scratches drastically by freeing particles from the rise of falling-out during an abrasive work through the process of filling or covering non-sintered parts and re-crystallized parts on the rough sintered surface by using electroplating process.
Thus, the object of the invention is to provide an abrasive dressing tool and a method for manufacturing the same tool wherein the rate of inferior polished products is reduced and the life time of the dressing tool is enhanced.
In conventional metal-brazed conditioner products, binding force is derived from carbides formed by chemical reaction between the diamond particles and the metal components including chromium or silicone. Therefore, the force for holding diamond particles is strong enough to ensure the long life time of conditioners, while the conditioners are associated with the drawback of causing scratches owing to falling-out of particles. In contrast, the electroplated products have smooth and neat surface so as to cause less scratches on wafers but have shorter service life.
In other words, the respective conventional conditioners were insufficient in that they have only one advantage. The products according to the invention, however, ensures the safety and long life time due to the prevention of falling-out for diamond particles and the high productivity due to the maximized decrease in scratch generation by provision of the both advantages as described above based on the double metal layers of the metal brazed layer and the electroplated layer.
Another object of the invention is to further increase the life time of conditioners by choosing the metal components of electroplated layers depending on the instance of application of the conditioners. As a practical example, the layers on wafers to be polished comprise sometime tungsten in a CMP process. In that case, a strong acid with pH of 2 to 4 is usually used as the slurry solution in polishing and therefore the conditioners can have the problem of abrupt decrease in life time because of the dissolution of sintered metal layers in contact with residual acid. In such a case, coating with the electroplated layer comprising the metal rhodium as a chemical resisting metal component can extend the life time of conditioners by two times that of conventional ones. It is one of major characteristics of the invention that an optimum conditioning effect in CMP process can be realized by adjusting the components of plated layers to a specific purpose, as illustrated in the above.
The above objects are achieved according to one aspect of the invention by a method for manufacturing an abrasive dressing tool, which comprises the steps of (1) coating the slurry solution of a brazing metal binder on a metal substrate to the desired thickness; (2) distributing super abrasive, cubic boron nitride or diamond particles in a predetermined amount on the slurry solution of (1); (3) heating the metal substrate of (2) as a whole in a hydrogen furnace or vacuum furnace at a sintering temperature between 700 to 1300xc2x0 C. depending on the kind of the metal binder used to fuse and fix the brazing binder so as to form a metal sintered layer; and (4) conducting electroplated coating only on the surface of sintered metal layer in order to fill or cover the rough parts and the non-sintered or recrystallized parts possibly to fall-out, those parts being present on the surface of sintered metal layer of (3).
The above objects are also achieved according to another aspect of the invention by an abrasive dressing tool usable for providing planarization polished surfaces requiring a high clarity like semiconductors, which comprises a metal substrate with a desired shape; a sintered metal layer formed on the metal substrate, the sintered metal layer being formed by mutual binding through sintering and brazing between uniformly distributed super abrasive, cubic boron nitride (CBN) or diamond particles and the nickel-based brazing metal; and an electroolated layer formed only on those parts except the exposed surface of super abrasive, cubic boron nitride(CBN) or diamond particles, out of the surface of sintered metal layer, the electroplated layer being formed by an electroplating process in order to fill or cover the non-sintered or re-crystallized parts present on the sintered metal layer.